Process for production of improved free machining steels



United States Patent Office 2,858,243 Patented Oct. 28, 1958 Elliot S. Nachtman,

Park Forest, 111., assignor to La Salle Steel Company,

ware

Hammond, Ind., a corporation of Dela- No Drawing. Application November 6, 1953 Serial No. 390,739

Claims. (Cl. 148-4) This invention relates to iron base alloys and steels having improved machinability and more particularly to steels and iron alloys, especially of the non-austenitic i type, formulated to contain elements which provide for marked increase in machinability characteristics, while, at the same time, also improving the physical and mechanical properties. While this invention has application particularly to steels, the concepts may also be embodied to improve machinability in alloy steels, iron base alloys and metals subject to machining operations.

It is an object of this invention to produce steels having improved machinability characteristics and it is a related object to produce steels and other iron base alloys 1 and metals of the type described embodying elements which impart marked improvement in machinability accompanied with improvements in physical and mechanical properties, without introducing limitations as to the processing characteristics for the formation of steel products. 1

Various means have heretofore been employed for the improvement of machinability in steel. In one of the earlier systems, machinability was improved by the addition of sulphur to steel. For such purpose, additions were made to insure that the content of sulphur in the finished steel would remain above 0.05 percent by weight, and generally within the range of 0.075 to 1.00 percent. The use of sulphur in such relatively large amounts for the purpose of improving machinability was found to introduce certain drawbacks and limitations with respect to the normal processing of the steel as by hot working or the like. It became necessary, for example, to make use of relatively high percentages of manganese in order to minimize or avoid brittleness and lack of strength of the steel at red heat.

In the past, use has also been made of phosphorus to improve the machinability of steels. While the increase in phosphorus tended to improve machinability of low carbon steels which are relatively soft and tend to drag during the machining operations, such additional amounts of phosphorus often resulted in excessive hardness and reduction in the ductility of the metal.

More recently, improvements in machinability have been found to result from the addition of lead, alone or in combination with sulphur or phosphorus. Use has been made of lead in amounts ranging from 0.03 to 1.0 percent by weight in the steel with marked improvements in the machinability characteristics. It has been theorized that the lead must remain as an elemental metal uniformly distributed as fine particles throughout the steel. For such. purpose, special precautions must be employed in the methods of incorporating the lead into the steel for improved machinability and for controlling the amount which remains and the distribution thereof.

Other elements, such as bismuth, antimony, tellurium, selenium and arsenic have been added to metals for the purpose of improving machinability but to the best of my knowledge no one before has employed any combinations of two or more of these materials or any other elements with any success except for the combinations which have been made, for example, to introduce both lead and sulphur or phosphorus. The combinations of lead and sulphur tosteel have been found to be complementary in an aggregative sense and are subject to limitation as to the amounts which can be introduced.

It has now been found, in accordance with the practice of this invention, that machinability may be increased unexpectedly by as much as two to four times that heretofore secured by the addition of lead, alone or in combination with sulphur and phosphorus, and that the strength properties, corrosion resistance and wear of the steel are also improved when copper is embodied as an element with lead, alone or in combination with sulphur and/or phosphorus within certain limitations in steel. I am aware of the fact that copper has: been used as an alloying element in the manufacture of alloy steels in which lead may have been used within the amounts previously described to improve machinability, I am also aware that copper may have been present in master alloys used to introduce lead into steel for the purpose of improving machinability, but no one, to the best of my knowledge, has ever before conceived and discovered that copper was elfective as an element which together with lead caused the machinability of steels to be improved far and beyond that ever conceived to be possible by the addition of lead or by the addition. of lead with sulphur and phosphorus. In most instances wherein copper has heretofore been intentionally introduced into steel as an alloying element, or when it has been present for the purpose of introducing lead as a'master alloy of copper, lead and tin wherein lead was believed to be the only element present to improve machinability, the amount of copper was so out of proportion and of such large amounts as to indicate clearly that the invention described and claimed herein was never conceived or suggested. In fact, the presence of copper in compositions of the type described was generally ignored because its presence was believed to constitute a necessary evil when introduced as a carrier. The relationship between copper and machinability has never, to the best of my knowledge, been recognized in the art and the use of copper hasnever been taught or suggested as a means to produce machinability characteristics in steel which are superior to any steels which have heretofore been manufactured. The novel results secured by the presence of copper together with lead to provide unexpected improvements in machinability may be illustrated by the following tables. For. the data listed below, the specimens for test were prepared of various melts of a medium carbon non-austenitic steel compounded in an electric furnace.

0 Mn P s Cold drawn 20%red. .44 1.61 .023 .290 .20 147 .42 1.42 .020 .030 .21 12 166 .41 1.40 .019 .930 .21 19 .09 291 It will be apparent from the above that by the addition of copper alone or of lead alone to a medium carbon steel of the type described, little or no beneficial efiect is achieved in the machinability index. However, the machinability index is increased over two to four times by the addition of both copper and lead in amounts corresponding to that used in each of the examples given above. It may be noted from the examples in group A that the high sulfur content had moderate beneficial effect which 1wag markedly increased in the presence of both copper and No explanation is yet available for this unexpectedly large increase in machinability secured by the addition of copper and lead together in amounts which separately were capable of only a moderate effect as regards machinability. Apparently a synergistic condition is established but the manner in which such synergism applies to improve the characteristics of the steel is not known. It is-known that lead is insoluble in the steel. It is also known that copper is soluble in ferrite in the steel and tends to harden the ferrite and that copper and lead are mutually soluble. It may be that the copper functions in combination with the lead to effect a more desirable distribution or arrangement of the solution in the steel or perhaps it functions in combination with the lead to introduce an entirely new relationship within the steel product. It appears that the improvements in machinability secured in accordance with this invention will be available from other elements capable of functioning as lead with copper in steels and iron base alloys of the types described and that improvements in machinability will also be experienced with other elements which function as copper in steel with lead.

Whatever the reason, it is apparent that the combination of copper and lead provides for machinability in steels, the type of which has not heretofore been available to the industry.

To the present, it has been developed that beneficial results are secured, in accordance with the concepts of this invention, when copper is present in amounts greater than 0.03 percent by weight and that the rate of improvement in machinability .increases appreciably at copper concentrations of 0.30 to 0.35 percent by weight. The minimum concentration of lead which is found to be effective with copper is about 0.03 percent by weight and the rate of improvement in machinability decreases appreciably when the concentration of the lead associated with copper reaches 0.50 percent by weight.

As previously mentioned, sulphur has its usual beneficial effect to further improve the machinability. The amount of phosphorus which may be employed in the composition along with the lead-copper combination, alone or in combination with sulphur, ranges from 0.01 to a maximum of about 0.2 percent by weight. t appears that manganese is effective also in combination with copper, alone or together with lead, preferably in the presence of sulphur, to improve machinability of steel. Improvements have been secured with manganese pres ent in amounts up to 2.25 percent by weight in the steel while the concentration of copper is maintained within the limits defined above.

It will be understood that the concentrations of the various elements may vary slightly depending upon the chemistry of the steel, iron base alloy or metal, and that use may be made of amounts beyond that at which a high rate of increase in machinability is secured.

The improvement in machinability'resulting from the combination of copper and lead in the desired concentrations in steels has been evidenced in the austenitic and the non-austenitic plain carbon steels as well as in the austenitic and non-austenitic alloy steels. It is believed that the improvements in machinability will also be secured in cast irons and other iron base alloys.

When copper and lead are present in the desired concentrations together in steels of the type described, improved machinability is secured independent of the processing steps employed for the preparation of the steel products, as represented by the improvements secured in hot rolled steel, in steels which have been reduced by con- I ventional cold working operations, in steels which have been cold worked followed by heat treatment in accordance with the teaching of the Landis patent No. 2,320,040,

in steels which have been worked and improved in their mechanical and in their physical properties by reduction at elevated" temperatures, as described in the copend ing applications Ser. No. 293,431, Ser. No. 293,432, and Ser. No. 293,433, all of which are now abandoned. The development of improved strength propertiesand Other mechanical and physical properties resulting. from working at elevated temperatures under the conditions described prevails notwithstanding the changes in chemistry of the steel to provide machinability by the addition of copper and lead and noticeable improvements are secured also as a result of the presence of copper and lead in steels processed in the manner described in corrosion resistance and in the wear resistance of the steel.

It will be apparent from the foregoing that a concept not heretofore recognized has been discovered to produce metals and alloys having'machinability characteristics far surpassing any which have heretofore been capable of being produced; I

It will be evident that copper, hereinbefore employed as an alloying element in steels or as a lead-copper-tin alloy for the purpose of introducing lead into the steel and which has never been recognized as favorably influencing machinability, has been found capable, when used with lead, of providing machinability characteristics far superior to that secured with lead, with lead and sulphur, or with lead, sulphur, and phosphorus, or with lead, sulphur, phosphorous and manganese, or with lead, sulphur, phosphorus, manganese and carbon, or other conventional combinations of elements for improving the machinability and for improving machinability far greater than is capable of being secured by either copper or lead alone in equivalent amounts.

In the machinability test for developing the data heretofore discussed, for evaluation of the steels, a constant feed is maintained during a turning operation. The force required to maintain constant feed during the turning operation varies depending upon the machinability of the steel. This variation in force constitutes a comparative measure of machinability.

It will be understood that changes may be made in the details of formulation and that the elements may be incorporated into the metals in various ways to give the desired results without departing from the spirit of the invention, especially as defined in the following claims.

I claim: 1

1. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in amounts ranging from 0.12 to 0.35 percent by Weight of copper and 0.03 to 0.5 percent by weight of lead, and subsequently machining the steel to produce'parts.

2. The metallurgical process for improving the machinability of steel comprising the steps of drawing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in amounts ranging from 0.12 to 0.35 percent by weight of copper and 0.03 to 0.5 percent by weight of lead, and subsequently machining the steel to produce parts.

3. The metallurgical process for improving the machinability of steel comprising the steps of extruding the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as es sential alloying elements in amounts ranging from to 0.35 percent by weight of copper and 0.03 to 0.5 percent by weight of lead, and subsequently machining the steel to produce parts.

4. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in combination with sulphur in amounts ranging from 0.12 to 0.35 percent by weight of copper, 0.03 to 0.5 percent by weight of lead and up to 1.0 percent by weight of sulphur, and subsequently machining the steel to produce parts.

5. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in combination with phosphorus in amounts ranging from 0.12 to 0.35 percent by weight of copper, 0.03 to 0.5 percent by weight of lead and 0.01 to 0.2 percent by weight of phosphorus, and subsequently machining the steel'to produce parts.

6. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in combination with manganese in amounts ranging from 0.12 to 0.35 percent by weight of copper, 0.03 to 0.5 percent by weight of lead and up to 2.25 percent by weight of manganese, and subsequently machining the steel to produce parts.

7. The metallurgical process for improving the machina'bility of steel comprising the steps of advancing the steel through a die to eflect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having a carbon content within the range of 0.4 to 0.6 percent by weight and having copper and lead present as essential alloying elements in amounts ranging from 0.12 to 0.35 percent by weight of copper and 0.03 to 0.5 percent by weight of lead, and subsequently machining the steel to produce parts.

8. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to eifect a reduction in cross-sectional area wherein the steel is a free machining steel of the 6 non-austenitic type having copper and lead present as essential alloying elements in combination with sulphur and phosphorus in amounts ranging from 0.12 to 0.35 per cent by Weight of copper, 0.03 to 0.5 percent by weight of lead, up to 1 percent by Weight of sulphur and 0.01 to 0.2 percent by weight of phosphorus, and subsequently machining the steel to produce parts.

9. The metallurgical process for improving the machinability of steel comprising the steps of advancing the steel through a die to effect a reduction in cross-sectional wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in combination with sulphur, phosphorus and manganese in amounts ranging from 0.12 to 0.35 percent by weight of copper, 0.03 to 0.5 percent by Weight of lead, up to 1 percent by weight of sulphur, 0.01 to 0.2 percent by weight of phosphorus and up to 2.25 percent by Weight of manganese, and subsequently machining the steel to produce parts.

10. The metallurgical process for improving the machinability of steel comprising the steps of heating the steel to a temperature within the range of 450 F. to the lower critical temperature for the steel composition, advancing the steel through a die to effect a reduction in cross-sectional area wherein the steel is a free machining steel of the non-austenitic type having copper and lead present as essential alloying elements in amounts ranging from 0.12 to 0.35 percent by weight of copper and 0.03 to 0.5 percent by weight of lead, and subsequently mashining the steel to produce parts.

References Cited in the file of this patent UNITED STATES PATENTS 1,964,702 Summers June 26, 1934 FOREIGN PATENTS 254,865 Germany Dec. 13, 1912 212,681 Switzerland Mar. 17, 1941 677,967 France Mar. 17,1930

OTHER REFERENCES Open Hearth Proceedings, vol. 38, 1955, pages 132 and 137. Published by the A. I. M. E., New York.

A. S. T. M. Standards, 1949, Part I, Ferrous Metals, pages 495 to 500. Published in 1950 by the American Society for Testing Materials, Philadelphia, Pa. 

1. THE METALLURGICAL PROCESS FOR IMPROVING THE MACHINABILITY OF STEEL COMPRISING THE STEPS OF ADVANCING THE STEEL THROUGH A DIE TO EFFECT A REDUCTION IN CROSS-SECTIONAL AREA WHEREIN THE STEEL IS A FREE MACHING STEEL OF THE NON-AUSTENITIC TYPE HAVING COPPER AND LEAD PRESENT AS ESSENTIAL ALLOYING ELEMENTS IN AMOUNT RANGING FROM 0.12 TO 0.35 PERCENT BY WEIGHT OF COPPER AND 0.03 TO 0.5 PERCENT BY WEIGHT OF LEAD, AND SUBSEQUENTLY MACHINING THE STEEL TO PRODUCE PARTS. 